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Biomedical subjects

Martin Garet

Publications and source records attributed to Martin Garet.

13 recordsLinked to original sources
PubMed2006

Modulations of human autonomic function induced by positive pressure-assisted breathing.

In order to examine the acute autonomic response in humans during and immediately after positive pressure-assisted (PPA) breathing, spontaneous cardiac baroreflex (BR) sensitivity was studied through the adaptation of consecutive RR intervals in response to spontaneous systolic blood pressure fluctuations in 11 healthy subjects. The gain (alpha-index) in baroreceptor reflex was estimated using cross-spectral analysis (RR interval variability and systolic blood pressure variability) for the low frequency (LF) and high frequency (HF) bands. All measurements were made under fixed breathing rate (12 breaths per minute), and realized consecutively at baseline level (20 min), after-short inspiratory pressure support plus positive end-expiratory airway pressure (IPS + PEEP) ventilation (15 min), again under normal conditions (20 min; recovery period) and, finally, during a standard upward orthostatic challenge test (15 min; orthostatic challenge). The spontaneous BR gain in the HF band increases slightly during ventilation (+26.1 +/- 11.7%, P<0.05) and decreases significantly during recovery without any significant alteration in mean heart rate, systolic or diastolic blood pressure. The spontaneous BR gain in the LF band decreases during IPS + PEEP ventilation (8.4 +/- 4.4 versus 12.7 +/- 6.2 ms mm(-1) Hg; P<0.05) and returns to basal level during recovery. Orthostatic challenge altered significantly the BR gain in both HF and LF bands with significant heart rate acceleration. In humans, while the parasympathetic control of heart rate and blood pressure is found moderately enhanced, the sympathetic BR drive appears significantly and transitory altered under short term IPS + PEEP ventilation with a degree of alteration comparable to those observed during orthostatic challenge.

Adult↗
PubMed2005

Interval training in elderly men increases both heart rate variability and baroreflex activity.

AIMS: Autonomic nervous system activity decreases continuously with age and appears to be a powerful predictor of disease and death. Attempts are thus made to reactivate autonomic drive with the intent of improving health. METHODS: We assessed maximal oxygen consumption (VO2max), autonomic nervous system activity by heart rate variability (HRV) analysis and spontaneous cardiac baroreflex activity (SBR) in eleven elderly men (73.5+/-4.2 years) before and after a 14-week program of intensive cycloergometer interval training. The standard HRV indices were calculated using time domain (mean RR, PNN50, RMSSD, SDNN, SDANN and SDNNIDX), and Fourier transform (total power, ULF,VLF, LF, LFnu, HF, HFnu and LF/HF) analyses of 24-hour, daytime and nighttime Holter recordings. The SBR was calculated from 15-minute recordings of spontaneous blood pressure and RR interval variations using the sequence (slope, slSBR) and cross-spectral (alphaSBRHF and alphaSBRLF) methods. RESULTS: After the training period,VO2max increased by 18.6 % (26.8+/-4.4 to 31.8+/-5.2 ml.kg(-1).min(-1), p<0.01). The nocturnal parasympathetic indices of HRV increased (PNN50: 3.05+/-2.21 to 5.00+/-2.87%, RMSSD: 29.1+/-7.6 to 38.8+/-10.9 ms, HF: 117+/-54 to 194+/-116 ms2/Hz, all p<0.05) as did the SBR indices (slSBR: 7.0+/-1.8 to 9.8+/-2.1 ms.mmHg(-1), p<0.01; alphaSBRHF: 6.9+/-2.2 to 10.5+/-3.7 ms.mmHg(-1), p<0.05; alphaSBRLF: 5.3+/-2.3 to 6.9+/-3.1 ms.mmHg(-1), p=0.22). CONCLUSION: Intensive endurance training in elderly men enhanced parasympathetic parameters of HRV and, interestingly, of SBR. Physiological mechanisms and long-term clinical effects on health status should be further investigated.

Aged↗
PubMed2005

Continuous positive airway pressure treatment improves the QT rate dependence adaptation of obstructive sleep apnea patients.

BACKGROUND: QT rate dependence is one of the major properties of ventricular repolarization, with its circadian and autonomic modulations. The alteration of cardiac autonomic tone occurring in obstructive sleep apnea syndrome (OSAS) patients could explain the altered rate-dependent adaptation of the myocardial repolarization. Thus, we postulated that dynamic alterations in QT interval adaptation could be ameliorated in OSAS patients under continuous positive airway pressure (CPAP) treatment. To assess ventricular repolarization features in patients with OSAS, we compared QT parameters and their dynamicities along RR intervals from 24-hour ECG. METHODS: The study groups consisted of 38 consecutive OSAS patients and 38 healthy age-matched subjects. The syndrome was confirmed for OSAS patients according to standard polysomnographic criteria (apnea plus hypopnea index: 56.9 +/- 28.4/h). A second polysomnography synchronized with 24-hour ECG Holter and realized under efficient CPAP therapy confirmed the control of sleep-related breathing disorder. RESULTS: QT length related to heart rate was found significantly altered in patients with OSAS compared with controls (QTend/RR slope: -0.126 +/- 0.031 vs -0.173 +/- 0.038; P < 0.01). This flattened relationship was significantly improved with the treatment of the OSAS (-0.151 +/- 0.051; P < 0.01 vs pretreatment status). There was no significant impact of CPAP therapy on ventricular ectopic activity as well as on static repolarization parameters (QT, RT, QTc, RTc) measured separately over daytime and nighttime. CONCLUSIONS: The prognostic implications of such findings and the protective role of CPAP treatment to prevent sudden cardiac death in OSAS need to be evaluated.

Analysis of Variance↗
PubMed2005

Relationship between daily physical activity and ANS activity in patients with CHF.

PURPOSE: Heart rate variability (HRV) indices are powerful independent prognostic factors of cardiovascular events and all cause mortality in patients with chronic heart failure (CHF). This study evaluates the influence of lifestyle on HRV in CHF patients. METHODS: Thirty-nine CHF patients (33 men, ischemic/dilated cardiomyopathy (18/21), 52.4 +/- 11.2 yr, NYHA I to III, LVEF 33.4 +/- 5.1%) filled out a physical activity questionnaire providing an individual complete qualitative and quantitative picture of their physical activity and daily energy expenditure (PAEE/DEE) corrected for age, weight, severity of the condition and autonomy. Frequency and time domain indices of HRV were calculated from ECG Holter recordings on a typical weekday. Nighttime indices were calculated in order to avoid the confounding factor of physical activity that might alter 24-h frequency analysis of HRV. RESULTS: DEE was significantly different between classes I and II and classes I and III (P = 0.01 both) patients. Time spent in activities above 3 METs decreased significantly with the severity of the condition. Global and parasympathetic indices of 24-h HRV analysis were correlated to DEE and PAEE (Ptot24h = 78.80*PAEE (J x min x kg) -1061.80, R = 0.72, P < 0.0001). Multiple regression analysis revealed that PAEE was the sole independent factor on established HRV prognostic indices (P < 0.05) and especially within PAEE dimensions, only activities above 3 METs were correlated with established prognostic HRV indices (P < 0.05). CONCLUSION: These results indicate that rather than total DEE, moderate to intensive physical activity may counteract the decline in HRV with chronic heart disease. This may be linked to longer time spent in higher intensity activities, and not to total activity time.

Adult↗
PubMed2004

Estimating relative physical workload using heart rate monitoring: a validation by whole-body indirect calorimetry.

Measuring physical workload in occupational medicine is fundamental for risk prevention. An indirect measurement of total and relative energy expenditure (EE) from heart rate (HR) is widely used but it has never been validated. The aim of this study was to validate this HR-estimated energy expenditure (HREEE) method against whole-body indirect calorimetry. Twenty-four-hour HR and EE values were recorded continuously in a calorimetric chambers for 52 adult males and females (19-65 years). An 8-h working period was retained, comprising several exercise sessions on a cycloergometer at intensities up to 65% of the peak rate of oxygen uptake. HREEE was calculated with reference to cardiac reserve. A corrected HREEE (CHREEE) was also calculated with a modification to the lowest value of cardiac reserve. Both values were further compared to established methods: the flex-HR method, and the use of a 3rd order polynomial relationship to estimate total and relative EE. No significant difference was found in total EE when measured in a calorimetric chamber or estimated from CHREEE for the working period. A perfect linear and identity relationship was found between CHREEE and energy reserve values for intensities ranging from 15% to 65%. Relative physical workload can be accurately assessed from HR recordings when expressed in CHREEE between 15% to 65%, and EE can be accurately estimated using the CHREEE method.

Adult↗
PubMed2004

A questionnaire-based assessment of daily physical activity in heart failure.

Type and dose of daily energy expenditure (DEE) play a major role in modulations of health status and an increased knowledge of these dimensions of physical activity in congestive heart failure (CHF) patients would be valuable for clinical and epidemiological aims. We propose a new self-administered DEE questionnaire adapted to CHF patients and tested its validity. One hundred and five stable CHF participants, NYHA class I-IV, LVEF=33.2+/-6.1% performed an incremental symptom-limited Vo(2) (peak) test and filled in the questionnaire for DEE calculation. Reproducibility (n=24), sensitivity (n=21) of the questionnaire and inter-observer variability (n=105) were tested. Intensity levels were identified from DEE and their relationships to Vo(2)(peak), ventilatory and anthropometric characteristics were assessed by simple and multiple regression models. Reproducibility and sensitivity were high (r=0.98 and 0.88, respectively, P<0.0001) and inter-observer error reached 1.37%. DEE was highly correlated to physical activity energy expenditure (r=0.96, P<0.0001). Relationships between DEE, Vo(2)(peak), V(E)/Vo(2) and anthropometric characteristics were significant. An activity level above 3 MET was the best intensity criteria related to Vo(2)(peak) (r=0.62, P<0.0001) and DEE (r=0.80, P<0.0001). The questionnaire seems reproducible, sensible and valid for DEE estimation. Vo(2)(peak) appears related to DEE and especially to activities above 3 MET in CHF.

Adult↗
PubMed2004

Chronotropic incompetence to exercise separates low body weight from established anorexia nervosa.

Chronotropic incompetence (CI), characterized by an attenuated heart rate (HR) response to exercise could participate to the limitation of exercise capacity in anorexia nervosa (AN). Therefore, we evaluated the role of cardiac sympathetic responsiveness in AN patients. In addition, the ambulatory value of autonomic control using spectral analysis of heart rate variability (HRV) was determined and correlated to maximal exercise performance. Twenty-two patients hospitalized for weight loss and suspicion of AN were included in the study. All performed a symptom-limited exercise test with measurement of gas exchange for chronotropic response to exercise evaluation. Holter ECG recordings allowed daytime and night-time spectral domain HRV analysis in order to evaluate the alteration of sympathetic control of HR in free-living conditions. CI defined as a failure to achieve 80% of heart rate reserve (%HRR) was observed in 13 (59%) patients (CI+). This group presented a higher body mass deficit than the group without CI (CI-; -35.1 +/- 8.7% versus -26.1 +/- 10.7%; P<0.05). Obviously, patients with a lower body mass index (BMI < 16 kg m(-2), n = 14) revealed a more severe limitation to maximal exercise with a lower peak HR, a lower peak Vo(2), and a lower maximal O(2) pulse (P<0.05). BMI was significantly correlated to peak Vo(2), maximal HR, and %HRR achieved at peak exercise. Daytime HRV parameters reflecting the sympathetic autonomic equilibrium (LF nu, LF/HF ratio) were significantly lower in CI+ patients. Blunted sympathetic response to maximal exercise is frequent and correlated to weight deficit. The present data suggest a major autonomic derangement in AN characterized by a cardiac sympathetic withdrawal.

Adult↗
PubMed2004

DAQIHF: methodology and validation of a daily activity questionnaire in heart failure.

PURPOSE: To assess the validity, reliability, and sensitivity of a new self-administered physical activity questionnaire estimating daily energy expenditure (DEE) in patients with congestive heart failure (CHF). There is a need to develop a low cost, practical, and accurate tool increasing the knowledge of the type and dose of physical activity in patients with CHF for clinical and epidemiological aims. METHODS: One hundred five participants with stable CHF performed an incremental symptom-limited VO2(peak) test and completed the questionnaire. For DEE calculation, time spent in each activity was multiplied by its energy cost corrected for weight, age, sex, autonomy, and the total was calculated over 24 h. Reproducibility and sensitivity of the questionnaire as well as interrater reliability were tested. Concurrent validity was assessed against VO2(peak), anthropometric characteristics and data from the literature. RESULTS: Test-retest correlation coefficients used to measure reproducibility ranged from 0.82 for activities ranging from 3 to 5 METs to 0.98 for DEE and a paired Student's t-test didn't reach statistical significance for any activity score studied. Interrater reliability was high with an error in DEE estimation of 1.37% (t value = -1.064; P = NS). Sensitivity (changes in VO2(peak) concurrent to changes in DEE) was high (r = 0.88, P < 0.0001). DEE was in line with the literature in patients with CHF and relationships between DEE and VO2(peak) (r = 0.71, P < 0.0001), and DEE and anthropometric characteristics (<0.0001) were significant. Activity level above 3 METs was the best intensity criteria related to VO2(peak) (r = 0.62, P < 0.0001) and DEE (r = 0.80, P < 0.0001). CONCLUSION: The questionnaire seems reliable, sensitive and valid for the estimation of DEE. VO2(peak) appears related to global DEE and more particularly to activities above 3 METs in patients with CHF.

Activities of Daily Living↗
PubMed2004

Individual Interdependence between nocturnal ANS activity and performance in swimmers.

PURPOSE: Variations in autonomic nervous system activity (ANS) and variations in performances have been shown to be correlated at the group level in swimmers. The aim of the study was to investigate the strength of that relationship at the individual level. METHODS: Seven regional-level swimmers (four male, age 16.6 +/- 05 yr, 6.4 +/- 0.9 yr of practice) were included in the study. They performed maximal aerobic performance on a 400-m freestyle race before and after a 3-wk intensive training period, and following a 2-wk tapering period. ANS activity was assessed through heart rate variability (HRV) indices measured the night before each race and twice a week along the protocol. RESULTS: All HRV indices were altered, with global and parasympathetic indices decreasing from W1 to W3 in the whole group, while they increased until W5 in five swimmers, and continuously decreased in two. Best performances were respectively realized when global and parasympathetic indices of HRV were highest. Importantly, the relationship between the changes in performances and the changes in HRV indices was strong (DeltaPerf = -1.232 to 1.625.DeltaHF(wavelet), R(2) = 0.5); the greater the rebound in ANS activity after W3, the greater the performance improvement, and reciprocally. CONCLUSION: Performance is correlated with nocturnal ANS activity at an individual level. The decrease in ANS activity during intensive training is correlated with the loss in performance, and the rebound in ANS activity during tapering tracks with the gain in performance. Interestingly, the speed of the rebound during the tapering period was quite different between swimmers. ANS activity measurement may be useful to design and control individual training periods and to optimize the duration of tapering.

Adolescent↗
PubMed2002

Quantification of cumulated physical fatigue at the workplace.

Quantification of physical fatigue remains a challenge. We hypothesized that its effects on central autonomic nervous system activity could be explored for such a quantification. To test this relationship, we prospectively measured central autonomic nervous activity through nocturnal heart rate variability (HRV) in six French garbage collectors, aged 32.1+/-4.3 years, twice a week during 3 consecutive weeks of work, and during the following week of rest. Eight healthy sedentary males formed a control group. HRV indices were calculated by applying standard temporal domain and wavelet transform analyses to standard ECG recordings. During the 3 consecutive weeks of work, there was a significantly progressive decrease in HRV indices, particularly pNN50 (-34.2%, P<0.05), as well as the high (-33.3%, P<0.05) and low (-22.2%, P<0.01) frequency components of wavelet transform, while there was an increase, although non-significant, of the ratio of low to high frequencies (9.1%). During the resting period, there was a significant recovery of HRV indices, notably of its high (50.0%, P<0.05) and low (28.6%, P<0.05) frequency components. No such changes occurred in the control group. A central signature of cumulated physical fatigue can thus be detected and quantified through nocturnal autonomic nervous system activity. Its characteristics are those of a progressive parasympathetic withdrawal.

Adult↗
PubMed2002

Cardiac baroreflex control in humans during and immediately after brief exposure to simulated high altitude.

To examine the baroreflex response in humans during and immediately after acute hypoxia exposure, the cardiac baroreflex sensitivity (BRS) was studied using adaptation of RR intervals in response to spontaneous systolic blood pressure fluctuations (sequences methodology) in 11 unacclimatized subjects. All measurements were made under fixed breathing rate, and realized consecutively at baseline level (20 min), at an inspired oxygen concentration of 11% (15 min) and again under normoxic conditions (20 min; recovery period). The spontaneous baroreflex response decreases progressively during hypoxic exposure, causing a tachycardic response at this FiO2 without any significant alteration of the systolic or diastolic blood pressure. The magnitude of decrease for this variable at the end of exposure averaged 42.9 +/- 15.6%. The simultaneous spectral analysis of heart rate (HR) variability in hypoxic condition confirmed an alteration in the parasympathetic activity (HFnu: -17.8 +/- 30.9% versus basal conditions, P < 0.01) counterbalanced by an exaggerated sympathetic activity (LFnu: +33 +/- 42.4%, P < 0.05) at the sinus node. Interestingly, we could observe an enhanced cardiac baroreflex response during the period following the inhalation of the hypoxic mixture (+130.6 +/- 15.6% of basal conditions, P < 0.001). There is a relationship with a significant and abrupt increase in the parasympathetic control of HR (mean HR reached 111 +/- 8.1% of the mean basal HR, P < 0.01). These results suggest that brief exposure to hypoxia under rate-controlled ventilation is associated with a significant alteration in the spontaneous cardiac baroreflex. This important cardiac autonomic imbalance is followed by a significant increase in the cardiac parasympathetic drive even after the disappearance of the hypoxic stimulus.

Adaptation, Physiological↗
PubMed2002

Autonomic adaptations to intensive and overload training periods: a laboratory study.

PURPOSE: Looking for practical and reliable markers of fatigue is of particular interest in elite sports. One possible marker might be the autonomic nervous system activity, known to be well affected by physical exercise and that can be easily assessed by heart rate variability. METHODS: We designed a laboratory study to follow six sedentary subjects (32.7 +/- 5.0 yr) going successively through 2 months of intensive physical training and 1 month of overload training on cycloergometer followed by 2 wk of recovery. Maximal power output over 5 min (Plim5'), VO(2) and standard indices of heart rate variability were monitored all along the protocol. RESULTS: During the intensive training period, physical performance increased significantly VO(2peak) : +20.2%, < 0.01; Plim5': +26.4%, < 0.0001) as well as most of the indices of heart rate variability (mean RR, Ptot, HF, rMSSD, pNN50, SDNNIDX, SDNN, all < 0.05) with a significant shift in the autonomic nervous system toward a predominance of its parasympathetic arm (LF/HF, LFnu, HFnu, < 0.01). During the overload training period, there was a stagnation of the parasympathetic indices associated to a progressive increase in sympathetic activity (LF/HF, < 0.05). During the week of recovery, there was a sudden significant rebound of the parasympathetic activity (mean RR, HF, pNN50, rMSSD, all < 0.05). After 7 wk of recovery, all heart rate variability indices tended to return to the prestudy values. CONCLUSION: Autonomic nervous system status depends on cumulated physical fatigue due to increased training loads. Therefore, heart rate variability analysis appears to be an appropriate tool to monitor the effects of physical training loads on performance and fitness, and could eventually be used to prevent overtraining states.

Adaptation, Physiological↗